fix(notifications/threads): Wave-1 audit fixes (🔴 + web 🟠)

- T1 (🔴): markThreadAsRead no longer receipts the thread ROOT (a 2nd instance
  of the read-marker-corruption regression — opening a thread whose root is old
  re-lit the whole room). Extracted to a pure threadReceipt.ts + 5 regression
  tests.
- N1 (🔴): favicon/tab-title unread count now sums only leaf rooms (was double-
  counting every ancestor-space aggregate in roomToUnread).
- N2 (🔴): notifications/sounds dedupe on the event id, not the unread count —
  fixes "read a DM, next message never notifies again".
- T4 (🟠): the thread notification path no longer re-gates on the room count, so
  an explicit per-thread "All replies" override in a Mentions-only room fires.
- N3 (🟠): getUnreadInfos skips phantom {0,0} entries (muted-thread-only rooms no
  longer light the nav row / pollute unread filters).
- N4 (🟠): the Receipt handler recomputes unread instead of blanket-DELETE, so a
  threaded receipt can't wipe a room's valid main-timeline badge.
- T2 (🟠): thread "Jump to Latest" re-anchors the virtual window (was landing on
  a stale mid/old event).

Gates: tsc/eslint/prettier clean, build OK, 678 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -11,7 +11,7 @@ import {
 } from 'matrix-js-sdk';
 import { focusAssistActiveAtom } from '../../state/focusAssist';
 import { manualDndAtom } from '../../state/manualDnd';
-import { roomToUnreadAtom, unreadEqual, unreadInfoToUnread } from '../../state/room/roomToUnread';
+import { roomToUnreadAtom } from '../../state/room/roomToUnread';
 import LogoSVG from '../../../../public/res/lotus.png';
 import LogoUnreadSVG from '../../../../public/res/lotus-unread.png';
 import LogoHighlightSVG from '../../../../public/res/lotus-highlight.png';
@@ -32,7 +32,7 @@ import {
   getUnreadInfo,
   isNotificationEvent,
 } from '../../utils/room';
-import { NotificationType, UnreadInfo } from '../../../types/matrix/room';
+import { NotificationType } from '../../../types/matrix/room';
 import { getMxIdLocalPart, mxcUrlToHttp } from '../../utils/matrix';
 import { useSelectedRoom } from '../../hooks/router/useSelectedRoom';
 import { useInboxNotificationsSelected } from '../../hooks/router/useInbox';
@@ -96,6 +96,11 @@ function FaviconUpdater() {
     let totalNotif = 0;
     let totalHighlight = 0;
     roomToUnread.forEach((unread) => {
+      // roomToUnread holds BOTH leaf rooms and per-ancestor space aggregates
+      // (leaves have `from === null`, aggregates a Set). Sum only leaves —
+      // otherwise a space-nested room is counted once as the leaf and again in
+      // every ancestor space, inflating the tab title / favicon count.
+      if (unread.from !== null) return;
       totalNotif += unread.total;
       totalHighlight += unread.highlight;
     });
@@ -232,7 +237,7 @@ function PresenceUpdater() {
 
 function MessageNotifications() {
   const audioRef = useRef<HTMLAudioElement>(null);
-  const unreadCacheRef = useRef<Map<string, UnreadInfo>>(new Map());
+  const lastNotifiedEventRef = useRef<Map<string, string>>(new Map());
   // Per-thread dedupe: threadId -> last notified eventId.
   const lastNotifiedThreadRef = useRef<Map<string, string>>(new Map());
   const mx = useMatrixClient();
@@ -367,17 +372,21 @@ function MessageNotifications() {
       const eventId = mEvent.getId();
       if (!sender || !eventId) return;
 
-      const unreadInfo = getUnreadInfo(room);
-      const cachedUnreadInfo = unreadCacheRef.current.get(room.roomId);
-      unreadCacheRef.current.set(room.roomId, unreadInfo);
+      // Dedupe on the event id (per room): the same event can re-fire (decryption,
+      // edit, thread repopulation). This replaces the old unread-COUNT dedupe,
+      // which suppressed a genuinely-new message whenever its post-read count
+      // matched the previously-notified count — i.e. "read a DM, next message
+      // never notifies/sounds" (the common one-at-a-time cadence).
+      if (lastNotifiedEventRef.current.get(room.roomId) === eventId) return;
 
-      if (unreadInfo.total === 0) return;
-      if (
-        cachedUnreadInfo &&
-        unreadEqual(unreadInfoToUnread(cachedUnreadInfo), unreadInfoToUnread(unreadInfo))
-      ) {
-        return;
-      }
+      // Main-timeline path respects push rules: don't notify when the room has no
+      // notification count (e.g. a non-mention in a Mentions-only room). The
+      // thread path is already gated by shouldNotifyThreadReply, so it must NOT
+      // re-gate on the room count — otherwise an explicit per-thread "All replies"
+      // override in a Mentions-only room is silently dropped.
+      if (!threadId && getUnreadInfo(room).total === 0) return;
+
+      lastNotifiedEventRef.current.set(room.roomId, eventId);
 
       const quietActive =
         focusAssistActive ||